Heating of meat causes certain physical chemical changes in muscle proteins which affect the quality of cooked meat and meat products. Changes in protein solubility, in the adenosinetriphosphatase activity of myosin, or in the contractibility of the muscle fiber have been used by others to determine the extent of denaturation of meat proteins. In this study the changes in the hydration of muscle were studied because this factor is more directly correlated with the quality of meat (28,31, 66, 67). It is known that heating releases juice, that the amount of juice depends on the temperature, and that this loss of water influences juiciness and texture of meat (4,28,36, 43, 66, 68). In this study we have investigated in some detail the influence of different temperatures on the hydration of beef muscle.An investigation of the influence of temperature on the pH-dependence of water-holding capacity will give information concerning changes in meat quality and also the mechanism of denaturation. This is because changes in protein net charge and in steric conditions affect meat hydration in a pH range from pH 3.0 to 7.5 (34).In addition we have determined the acidic and basic groups in muscle and the solubility of the globular and structural muscle protein after heating at different temperature. METHODSUtility cows from 4 to 6 years of age were used. Two to 3 lb of the longissimus dovsi muscle were cut from the carcass 5-6 days after slaughter. Connective tissue and fat were removed as far as possible. The muscle was ground twice in a cooled meat grinder.Influence of pH on the water-holding capacity of meat after heating at different temperatures.One hundred g of ground meat at 20" C was minced in a homogenizer with 30 ml ice water at high speed for 30 sec. During mincing the metal homogenizer vessel was cooled by ice.For heating meat, the covered metal vessel of a homogenizer, filled with 110 g of ground meat, was placed in a water bath of the desired temperature.The meat was heated with occasional stirring until it was at the temperature of the water bath and was kept there for 30 min. [Other authors have shown that after 30 min heating at 70-90" C protein hydration changed very little (43, 6011. Then the vessel with meat was put in ice for about 15 min. Thirty-three ml ice water was added to bring the added water to 30%. The mixture was minced in an ice-cooled homogenizer in the same way as the fresh meat. It was considered that the different texture of heated muscle has an influence on the extent of mincing and, therefore, oh the water-holding capacity; however, we found that this effect has no influence on the relative difference of hydration produced by heating.

The only esters detected in the Fleischmann pre-ferment were those of acetic acid. The ethyl ester was presumably produced because of the high concentration of ethyl alcohol in the fermentation mixture. Wiseblatt (26) found only ethyl esters in bread crumb.The change in ethyl acetate concentration in the pre-ferment with time is shown in Figure 2. The ester reached its maximum concentration after 6 to 8 hours of fermentation and decreased to zero after 48 hours. The concentration of ethyl acetate in American Dry Milk Institute pre-ferments was not determined because it was necessary to adjust the pH of that pre-ferment to 10.0 to precipitate a part of the nonfat dry milk.

An apparatus for the study of the autoxidation of fats and related materials has been designed to permit the collection and analysis of the various volatile products formed in the reaction, the measurement of the oxygen consumption, and analysis of the oxidation residue.Oleic acid, oleyl alcohol, methyl oleate, butyl oleate, and cis-9-octadecene appear to he autoxidized in a similar manner to yield the same types of products-among others, peroxides, peracids, aldehydes, substituted ethylene oxides, acids, alcohols, combinations of these, and water.After the addition of oxygen to form peroxides at the ethylene linkage, these peroxides may cleave to give aldehydes; they may react with another double bond to give two moles of ethylene oxide;or they may aid in the further oxidation of the carbon chain. The aldehydes formed also autoxidize to give peracids and acids.

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The relation between the changes of hydration and the changes in charge of muscle during the heating of meat has been reported previously (13). This investigation showed that it is possible to study the protein denaturation of meat by means of the determination of its water-holding capacity and its buffer capacity at different pH values and of the amount of dyes bound by the acidic and basic groups of the proteins. In the present paper these methods are used to determine whether freezing and thawing cause denaturation. This problem was of interest because of the undesirable changes in meat proteins brought about by freeze drying (10). In this process the meat is frozen before drying and the question arises whether changes caused by freeze drying are due to the freezing procedure itself or to other factors.It is known that freezing immediately after slaughter presents special problems because of the presence of adenosinetriphosphate (ATP) and the accelerated decomposition of the ATP during thawing resulting in "thaw rigor." In order to prevent such influences of ATP, for all experiments meat was used 5 to 6 days post mortem, after resolution of rigor mortis.

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